This invention relates to an improved process for preparing hexafluorothioacetone dimer by reacting hexafluoropropene with an alkali metal fluoride and sulfur in a selected aprotic solvent and specifically to the use of an aprotic solvent comprising acetonitrile, dimethylacetamide, dimethylformamide, dimethyl sulfoxide or N-methyl pyrrolidone.
The preparation of hexafluorothioacetone dimer by reaction of hexafluoropropene with sulfur and alakli metal fluoride such as KF in tetramethylene sulfone or nitrobenzene at a temperature of 120.degree. to 150.degree. C. in an autoclave under elevated pressures is disclosed by B. L. Dyatkin et al., in Proceedings of the Academy of Sciences of the USSR, 183, 1018-1021 (1968), and by B. L. Dyatkin et al. in Tetrahedron, 29, 2759-2767 (1973). However, the use of elevated pressures and high temperatures requires special equipment. Since both references report production of other products such as oligomers of hexafluoropropene and compounds containing the perfluoroisopropylthio group, the process becomes involved with increased separation steps and expense, and the overall yield of hexafluorothioacetone dimer is lowered.
Another method for preparing hexafluorothioacetone dimer by reaction of hexafluoropropene with sulfur over an activated carbon catalyst at 425.degree. C. is disclosed by K. V. Martin, J. Chem. Soc., 2944 to 2947 (1964). However, the high temperatures required makes the process economically unattractive.
Hexafluorothioacetone dimer [2,2,4,4-tetrakis(trifluoromethyl)-1,3-dithiethane] is an intermediate in the production of hexafluoroisobutylene, and of hexafluoroacetone which is useful as an insecticide and for the preparation of high molecular weight polymers.
In the course of development of the process of the present invention, it was discovered that the reaction of equimolar proportions of hexafluoropropene and sulfur in the presence of potassium fluoride and tetramethylene sulfone at atmospheric pressure conditions did not result in formation of hexafluorothioacetone dimer.
Accordingly, it is an object of the present invention to provide a process for the preparation of hexafluorothioacetone dimer by reaction of hexafluoropropene with sulfur and alkali metal fluoride in a suitable solvent at atmospheric pressure conditions.
This and other objects and advantages of the present invention will be apparent from the description which follows.